Cross-country and telemark ski bindings, referred to herein as “touring bindings” are designed for use with a ski boot which is sufficiently flexible near the ball of the user's foot to permit the boot to flex upwards and forwards while the toe of the boot remains fixed on the surface of a ski. This permits the user to perform a relatively normal walking motion while travelling uphill or on flat ground and to lift the heel of the boot from the ski in order to perform a telemark-style turning maneuver. Traditionally, such boot flexibility was provided by the materials from which the ski boot was constructed. For example, a ski boot with a leather upper can be quite flexible. Also, boot soles comprising a combination of leather and rubber are also quite capable of flexing near the ball of the foot. More recently, the uppers and soles of telemark ski boots have been constructed from synthetic plastic materials which are less flexible than leather or rubber. To compensate for the use of synthetic materials, modern telemark boots will typically include a compressible bellows in the upper portion of the boot near the ball of the foot which allows flexing of the boot.
A touring binding will comprise a toe piece adapted to hold the toe of the boot at an appropriate location on the upper surface of the ski while leaving the heel portion of the boot free to rise above the ski surface. Some designs of cross-country bindings provide means such as a clamp or pins for fixably retaining the toe of the boot within the toe piece. However, other designs which lack means for such fixing the toe of a boot in the toe piece make use of a cable, bail, or cable and bail combination which extends around the heel of the boot to provide constant tension whereby the boot is urged forward into the toe piece and is retained. Such cable and/or bail assemblies have also been employed to reduce lateral movement of the heel of the boot and to provide means for biasing the heel of the boot towards the ski surface in order to obtain better control of the ski, particularly during downhill skiing.
Tension is typically provided in the aforementioned cable and/or bail assemblies by one or more springs. For example, the binding may comprise a spring-loaded lever mounted to the ski forward of the toe piece to which a cable assembly is attached. Movement of the lever will shorten the rearward extent of the cable relative to the toe piece thereby tensioning the cable about the heel of the boot. In other versions, the lever may be present elsewhere, for example on or near the heel of the boot. Springs may also be situated elsewhere in the assembly, such as at intermediate coaxial positions in the cable/bail assembly alongside or underneath the boot. Springs employed in such bindings include those which operate while under tension (i.e. the spring is stretched while in use) as well as spring assemblies in which a compressed spring provides a directed force which tensions the cable or bail assembly. Regardless of the nature of the spring(s) or their location in the ski binding, employment of synthetic plastic materials in telemark boots has permitted the use of springs which provide for greater tension without buckling or significantly compressing the boot than springs traditionally used with leather boots. This gives the advantage of greater stability during turning and in other downhill maneuvers.
Upwards and forward flexing of a boot in a touring binding results in the sole of the boot adjacent the ball of the foot lifting from the surface of the ski. Since the cable and/or bail assembly is fixed or hinged at selected points on the toe piece, such upward movement of the boot generally results in increased tension being applied through the cable/bail assembly to the heel of the boot while the boot rises. While this greater tension serves to bias the heel of the boot downwards and thereby provides some stability for certain maneuvers, such an increase in tension must be overcome by the user while walking and travelling uphill. When stronger springs are employed, the user will have to perform greater work in lifting the heel of the boot during walking and uphill travelling motions. Even in bindings designed to minimize the difference in tension while the boot flexes, use of higher tension levels to provide downhill stability will increase the bias of the boot towards the ski surface at all flex positions. This can be disadvantageous while climbing uphill using climbing skins since the bias effect tends to lift the ski from the snow surface as the boot flexes forward. With climbing skins, the user may wish to maximize contact with the snow to reduce backwards slippage.
Traditionally, the heel counter of a ski boot extends rearwards some distance and is separated from the boot upper by a welt. This provides an upward facing ledge extending around the circumference of the upper portion of the heel counter and is often used to engage a ski binding element. This feature is often retained in modem plastic ski boots and is included in the I.S.O. standards for ski boots (e.g. ISO 9523:1990). The welt is often retained as a feature on plastic boots employed for cross-country and telemark purposes, but not always. Nevertheless, all cross-country and telemark boots designed for use with cable/bail assemblies will at least have a lateral groove formed around the circumference of the heel counter of the boot below the level at which the welt typically appears. This groove is typically used for placement and engagement of a cable or bail of a touring binding or for placement of a tensioning lever.
Tensioning levers have been employed for many years to retain a cable and/or bail on the heel of a ski and boot. Such cable and/or bail assemblies with tensioning levers have been found in alpine-style bindings in which the heel is continually retained against the surface of the ski; in alpine-touring bindings in which a rigid boot is retained against a plate or bar hinged at the toe of the boot to the ski surface thereby permitting the rigid boot to rise above the ski surface; and, in touring bindings used with flexible boots. Such tensioning levers have also been employed to retain cable or bail assemblies on the heel of boots in other applications such as the case with “step-in” style crampons which are intended to be attached to the full length of the sole of a mountaineering boot without any tendency for separation of the crampon from the boot sole during use.
Tensioning levers operate on the “over-center” principle. The lever will typically comprise a handle portion opposite a portion shaped to engage or clamp a ledge, groove, or other feature on the heel of the boot (a “boot holder”). The lever is rotationally engaged on the cable or bail at a pivot location situated between the handle and the boot holder. The lever is arranged so that when the boot holder is placed on a boot feature and the lever is rotated by means of the handle (typically upwards), the boot feature will come under clamping engagement while the pivot is displaced from a series of positions which place zero, then high, then moderate tension on the cable. The lever retains the cable on the heel of the boot because in order to reverse rotation of the lever thereby releasing it from the boot, the tension on the cable must pass from the moderate to the high tension positions as the lever again passes “over-center”, the boot is released. An example of a modem touring binding which employs a heel tensioning lever is the TARGA™ binding produced by G3 Genuine Guide Gear of North Vancouver, British Columbia, Canada. Another example of such a touring binding is the HAMMERHEAD™ binding produced by Rainey Designs of Wilson, Wyo. U.S.A.
The tensioning lever of the HAMMERHEAD™ binding referenced above is designed to assist the user in locating the lever in the lateral groove of a boot heel. This lever, which has been referred to as having a “beaver tail” design consists of a standard lever handle, boot holder means, and a pivot therebetween. Adjacent the boot holder and extending away from the pivot point opposite the handle is a plate provided as a separate element which is removably attached to the lever by means of a fastener. The binding bail assembly is adjusted so that when the user places a boot into the binding with the heel lever rotated backwards and flat to the ski, the heel of the boot will clear the boot holder portion yet contact the plate. The distance between the plate and the heel holder portion is such that once the boot contacts the plate and the user rotates the lever upwards by pulling on the handle, the heel holder will automatically locate and engage the lateral groove of a standard telemark boot heel. In order for the plate to be effective, it must extend away from the pivot the same distance as the heel holder. A different apparatus with a similar boot locating function is found in the V-CAM™ of Voile Equipment (USA) where the heel tensioning element comprises a semi-circular rocker with a boot holder portion and a plate extending from the pivot as far as the boot holder. Stepping on the plate causes rotation of the rocker which automatically engages the heel holder with the lateral groove of a boot heel.
In the past, users of touring bindings that employ a tensioning lever may have compensated for resistance to boot flexing caused by binding tension during walking and uphill maneuvers by rotating the lever past the “over-center” point, thereby disengaging the boot holder from the boot heel. If the overall length of the cable or bail assembly permitted, a surface on the lever other than that which is adapted to clamp the boot might be loosely engaged with a feature on the boot heel keeping the cable/bail from coming to rest on the ski surface and to some extent, preventing the boot from moving rearwardly. In bindings where the cable or bail assembly is the only means for retaining the boot within the binding, such loose engagement would not prevent the boot from becoming completely detached from the binding when significant forces were exerted by the user (such as when kicking or lifting the ski).